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Topic Title: Double and reinforced insulation
Topic Summary: Definition
Created On: 31 December 2012 12:11 PM
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 31 December 2012 12:11 PM
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Zs

Posts: 2861
Joined: 20 July 2006

Morning,

I'm sat here checking a ream of installation certificates which relate to a commercial building and have been issued by the installer prior to my inspection. They are mostly for replacement DBs. I know the building but haven't actually seen the completed boards yet. Interestingly, Rutts....they are all on your forms.

In the first section of the schedule of inspections, method of protection against electric shock, the installer has ticked the boxes for Double Insulation and Reinforced insulation.

I know that the boards are fed with SWA from the intake room.
I know that most of the installation is in Twin and Earth, embedded in plaster and that some of it is in plastic conduit. there is a bit of FP200 there. Very little steel conduit.

I'll save you the trouble of looking it up:
Double insulation: 'insulation comprising both basic insulation and supplementary insulation'
Basic insulation: ' insulation applied to live parts to provide basic protection and which does not necessarily include insulation used exclusively for functional purposes.'
Supplementary insulation: 'Independent insulation applied in addition to basic insulation for fault protection'
Reinforced insulation; 'Single insulation applied to live parts which provides a degree of protection against electric shock under the conditions specified in the relevant standard...

I would not have ticked either of the boxes for double or reinforced insulation, but I'd like to check that with you before giving any feedback. the definitions are a bit flimsy. I think the installer might be thinking that the SWA feeding the boards qualifies as double and reinforced. However, in my view at the moment, the installation as a whole is not double or reinforced, and neither is SWA, although I suppose we could argue that for sport.

I'm inclined to get him to untick those boxes. Do you agree?

Zs
 31 December 2012 12:22 PM
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John Peckham

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Zs

Any Class 2 light fittings?

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 31 December 2012 01:01 PM
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daveparry1

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I think i'd say t/e is double insulated Spin? I wouldn't think the cpc being un-insulated would mean it wasn't a double insulated cable, not sure about this though, never really thought about it,

Dave.
 31 December 2012 01:11 PM
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perspicacious

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I'm waiting for the post commenting on the practice of glanding off SWA and taking the remaining innards outside the glanded enclosure......

Regards

BOD
 31 December 2012 01:25 PM
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rocknroll

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None of the cables you use are double insulated, insulated and sheathed is the correct term, the grey covering on T&E and most tails is an abrasion resistant material to protect the insulated conductors from damage, with armoured cable the armour is to protect the whole cable and the sheath over the insulated conductors is to protect them against the abrasive armour.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 31 December 2012 01:35 PM
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perspicacious

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"With T&E, the live conductors are double insulated from external earth sources, by means of the conductor insulation and the sheath."

Does BS 6004 require the sheath to undergo an insulation test during manufacture?

Regards

BOD
 31 December 2012 01:55 PM
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Zs

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JP, I don't know about class 2 fittings yet. I remember the ceiling lighting was egg-box modular recessed but not sure about the loos for example.

I have never even considered tails to be double insulated but ready to be corrected.

Zs
 31 December 2012 02:07 PM
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rocknroll

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From a technical point of view UK installations are by law required to be 400/230V basic insulation and earth to the electrical outlet and this is what all your protection arrangements are based on, the outlet deemed as the wires that stick out of the wall, ceiling whatever, the outlets, shaving transformer, lighting transformers, sockets, switches, lights etc; are all covered by seperate standards basically being suitable to be connected to a 400/230V basic insulation and earth system.

So from a technical point of view all of these boxes;
SELV
PELV
Double or Reinforced Insulation,
should carry a N/A as it refers to the installation as pointed out above.

Irrespective of what you connect to the electrical outlet your installation is still protected by basic insulation and earth, there are installations by special arrangement that are double and reinforced insulation which requires no earth, reserved for establishments where the presence of an earth could compromise the operations through monitoring or disruption, such is the technology today.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 31 December 2012 02:08 PM
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daveparry1

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Oh yes, tails are (or should be!) double insulated Zs,

happy new year to you,

Dave.
 31 December 2012 02:10 PM
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tattyinengland

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I'd have ticked the box for double insulated if there was class two equipment or conventional household distribution board type tails.

I'd say that Re-enforced insulation = artic cable or similar toughened outer sheath.
 31 December 2012 02:16 PM
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rocknroll

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Originally posted by: perspicacious

"With T&E, the live conductors are double insulated from external earth sources, by means of the conductor insulation and the sheath."

Does BS 6004 require the sheath to undergo an insulation test during manufacture?

Regards

BOD


Good point that should not be missed, is the grey covering on T&E and tails tested for its insulation properties or is it tested as low abrasion protective covering.????

Answers on a postage stamp please.!!!

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 31 December 2012 02:18 PM
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alancapon

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Originally posted by: Zs
. . . I have never even considered tails to be double insulated . . .

I agree. I believe that Meter Tails are "insulated & sheathed", just like twin & earth, although a lot of people refer to them as "double insulated". Where they win over twin & earth, is that each core has its own sheath, it is therefore less likely to have a core-to-core fault.

Regards,

Alan.
 31 December 2012 02:28 PM
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Zs

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Oh Dave, we may be about to disagree for the first time everrrr.

How are tails double insulated? I'm thinking of double insulation like in Portable appliances, where there is an enclosure of insulating material between the live part and the outer insulation. Happy to be wrong, it is why I am asking the question.

In this case I am pretty sure I am going to encounter SWA feeding the boards, as it was when I recommended the DBs be changed.

As an extra question; If the building turns out to have, for example, a single double insulated light fitting and hundreds otherwise, would you still tick the double insulated box?

Zs
 31 December 2012 02:39 PM
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daveparry1

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But surely Zs if the tail has a layer of insulation covering the wire and another layer covering the insulation that makes it double insulated? Quite often the outer layer is grey whilst the inner layer is blue or brown, although the old black and red tails usually had the same colour for both layers,

Dave.
 31 December 2012 02:51 PM
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Zs

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Don't know Dave, and you may turn out to be top banana as usual. It may well be that I should have been ticking those boxes myself for years. Seeing them ticked has alerted me to check this.

In non technical terms I think tails, with their two layers right up against each other are stil prone to being damaged by pressure or a sharp point and the live cores becoming exposed.

If I smack a hole in the side of a double insulated drill or transformer though, there is still more insulation before I can get my fingers on the live parts.

Something like that, hopefully some of you can see where I'm coming from and there's a classic example of why I don't do well in exams.

Zs
 31 December 2012 03:02 PM
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Parsley

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I've never ticked this box, I might if I had a TT install with reinforced/double insulation equivalent meter tails running into a metal enclosure/trunking before the RCD, so a fault could not develop on the earthed metal work.

But if it's the only form of protection throughout an installation it should only be used with adequate supervision.

Regards
 31 December 2012 03:09 PM
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spinlondon

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 31 December 2012 03:15 PM
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daveparry1

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I think this might mean we agree on something Spin!

happy new year mate,

Dave.
 31 December 2012 03:18 PM
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Zs

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Then should they not be embossed with the double insulated symbol of the two squares and carry all the usual ramifications? Sorry Spin, I'm doubting and thinking the term is generic. Still not sure about this.

Zs
 31 December 2012 03:19 PM
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daveparry1

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top banana as usual
-------------
I wouldn't go that far Zs, there are plenty of people on here that disagree with me on various things! As for the double insulation issue, i'm just reading it as English grammar, ie double meaning two, not necessarily true where regulations are concerned perhaps,

Dave.
IET » Wiring and the regulations » Double and reinforced insulation

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